Process for making tetrachloro-p-xylene



SePt- 27, 1950 E. A. swAKN Erm. 2,954,409

PROCESS FOR `MAKING TETRAcHLoRo-P-XYLENE Filed Aug. 29, 195s @In QQQQ QNmbk QS nited States Patent `PROCESS' FOR `'MA-K1N G TETRACHLORD-p-4XYLENE `Edward A. `Swakon, Hammond,.and .Richard "Van `Strien,Griiiith, 1nd assignors to Standard Oil .Comrpany, Chicago, Ill., acorporation VAol? Indiana Filed Aug. 29,' 1958, Ser. No..-758,100

"'Ihisinvention-.rlates to .tetrachlorofpfxylene vandfparticularlyanimproved processfor this. compound. l*

`ferredf toavoid the` presence Aot ,slid tetraehlorofp-xylene .initheschlorinationzone, the. amount of chlorine added 'fis adjustedtoobtain a product solution containing tetra- Vchloro-p-xylene inanamount. no ,greater than'itssl-u- Hbility at .the chlorinationzone'temperature.

. The chargeto the chlorination zone maybep-xylene .'itslf `or a ylowerchloro-pfxylene'or mixture of these. Ihe lower chloro-pfxylenes are.understood to bechlo'rinated p-xylenes containing'l, 2 or 3 chlorinenuclear substituents such as monochlorofp-xylene,fdichlofrorp-xylene yThe chlorination reaction .is carried outpreferably in fthepresence offachlorination cataly'strsuch as metallic iron powder oriron chloride orany. of the catalysts. conventionallylknown to be electivein.chlorination reac- FCC -2 fchlorobutenel, `1,2','3trichlorobutane,2,2;3-trichlorobutane, and 111,'1,2Ltetrachlorobutane.

The chlorination maybe carried out at temperatures arldpressures such asare conventionally used. In "gen- Feral, the chlorination zonetemperature isv maintainedibe- "tween about 40 C. and 150 C.; in thecase of the'lower boiling members .of the class of defined solvents, 'it.is customary to operate atta temperature corresponding to'thereux'ternperaturelof the solution existing in #the chlorination zone. Ingeneral, it is preferred to `operate the..chlorination zone `at .atemperature between about '60`C. and'90"C.

'The amount of chlorine addedto,thechlorination'zone adjusted toproducea mixture ofehloro-'p-xylenes; which lniir'rturecontains an amount ofthe lower chloro- .p-'Xylenes Vless than the saturationcontent'ofthesolution, at the Y temperatureto `which .the productsolution isto be cooled sii-bseguenttothe chlorination reaction. Theamountof chlorine addedmay result in vtheproduction `of'an amount f.tetrahlorp-xylene in-excess Lof the saturation limit of theslu'tionkat'fthe chlorination zone temperature. `llt 'isprferreldto -adjust'theamount of chlorine addedto produce an amount f Atetrachlorofplxylene inexcess Yof that soluble yinthe solution at the temperature towhich 'thepro'ductsolution istolbe cooled .and on ytheorder of 'the solubilityintheproduct solution at the chlorination .zone temperature.

'Iheproduct solution .comprises t-he chlorinated VAhydroca'rbon solvent,.chlorinated p-xylenes and unreacted jp- ,ya mixture of lower.chloroap-xylenes.

.xylene, if pxylene was present in the charge. The chlorinatedp-xylenescomprise tetrachloro-p-Xylene and This productco- 'lutionffromthe-chlorination zone is cooled tof altemperature :Such that crystals,of Vtetrachloro,-'plxylene.areforrned defnedclass of solvents, whichboils at about the de- `sired chlorination Zone temperature. LBythismeans, it

l is possible to carry out the vchlorination at'thedes'ired.chloroethana'tetrachloroethylene, n -propyl Chloride, 1,1-

dichloropropane' 2,2-dichloropropane, y'l,1,"21trichloropropane,^1,1',3'trichloropropane, `1;1,l,2tetrachloropropane,

` '1,2,2,3etetrachloropropane, 1,l,2l33fpentachloropropane,

Y as essentillytheonly solid product i.e. 'the' temperature suh"t.hatthe saturation point of the, pro'duct"solu'tion withrespect to anyfrthedower chloro-plxylenesipresent is not reached. 4In general, theproduct solution: is cooled to a temperature Within ordinary`atmospherictemperature range, namely,J between about 0C. ar1d'40- l C.and morevusullybetween about'l5 VC..,a.n'd 30 '^C. The vsolid producttetrachloro-p-xylene "is separated ,from a nliquid solution of reduced'tetrachlorp-.xylene content. v4If essentially pure.tetrachlorogp-xylene Eis desired, "the crystals may be Washed withfresh solvent to remove ad- .hering solution. 'The .separated.solutionan'd wa'shings may be recycled to the chlorination Zone.

The .crystals of solid tetrachlorop-xylene mayberse'p- .arated 'from themother'liquorr by 'decantatiom filtration, rcentifuging orany of "theconventional proceduresjfor `separatingliquidfrorn'solid, withoutresorting to vaporization -Theffollowing illustrates the very, verygreat difference vlin capacity of the'tdenedclass of chlorinatedaliphatic hydrocarbonsfor lower chloro-p-Xylenes and tetrachloro- 4Vp-xylene. .fAt 25 C. 'dichlorofp-xylene 'is soluble ,in .chloroform tothe extent of '34 grams per'100 ,gramsof solvent andQin"tetrachloroethylene to the extent o'f :31 grams` perl'00 grams ofsolvent. Trichlororp-xylene at 25"CQis solublein chlorformto'theextentof 4`0 grams lper 100 grams of solvent and'in tetrachlorothylene'to.c'lil'orogpfxyleneSaatIv 25 1C. is soluble in chloroform ',toVtheJer'i-tent of 3 ,gramsper1l`00 grams,in carbon'tetrachlorideto`the.extent,of-3 gramsper 1ML-grams andfin tetrachloroethylene'to 'theextent of 4^grams. 'The solubility of .tetrachlorop-xylene at Atheboiling `poirit of 'chloroform(61'`CI) is "13' grams per'TOO gramstfslvent; the solubility in carbonJtetrachloride at it'sbiling point (77C.) is l1 grams per 100 grams of solvent; the 1 solubility.-inttetrachloroethylene at 1100" :is :'.w'll in.excesslotgramstper:grams.of;solvent. i

An illustrative embodiment of the process is set out in conjunction withthe annexed gure. The ligure is schematic and many items of processequipment have been omitted which can be added by anyone of ordinaryskill in this art. It is to be understood that the embodiment is notlimiting on the scope of the invention. In the figure the chlornationreaction is carried out in reactor 11. Reactor 11 is provided with amotor driven stirrer 12 and baffles, not numbered, which permit eicientagitation within reactor 11. In this embodiment nitration grade p-xyleneis added from source \13 by way of valved line 14 and line 16 into thebottom of reactor 11. Chloride from source 17 is passed by way of valvedline 18 and line 16 into reactor 11. Recycle material is passed by wayof lines 19 and y16 into reactor 11. Ferric chloride catalyst is addedperiodically from source 21 by way of valved line 22 into reactor 11.

|In this embodiment the solvent is carbon tetrachloride. Thechlorination reaction is carried out at the reux temperature of thesolution existing in reactor 11, which is about 80 C. The amount ofchlorine added is such that all of the tetrachloro-p-xylene producedremains in solution at chlorination temperature. In general, when carbontetrachloride is the solvent, the solution produced in reactor 11preferably contains from about 7 to 10 grams of tetrachloro-p-xylene per100 grams of carbon tetrachloride in the solution.

Reactor |11 is operated at atmospheric pressure. The product HCl andcarbon tetrachloride vapors pass out of reactor 11 by way of valved line23 into condenser 24.

The HC1 is passed from the system to a vent or recovery by way of valvedline 26. The liquid carbon tetrachloride produced in condenser 24 isreturned by way of line 27 to reactor 11. Reactor 11 is provided withdraw-oli line 28.

Product solution comprising carbon tetrachloride andtetrachloro-p-Xylene is continuously withdrawn from reactor 11 by way ofa trap-out 29 and passing by way of line 31 into cooler 32. In cooler 32the product solu- -tion is lowered in temperature to about 25 C. The

cooled product solution is passed by way of line 33 into crystallizer34.

Crystallizer 34 may be any conventional form of- Y crystallizing vesselsuch as the coned-bottom vessel provided with a baille 36 as shown here.In crystallizer 34 solid tetrachloro-p-xylene settles out of the secondsolution, i.e., mother liquor, which contains essentially all of thelower chloro-p-xylenes present in the product solution. The crystals oftetrachloro-p-xylene are withdrawn from crystallizer 34 by way of line37 and passed into centrifuge 38.

Centrifuge 38, in this embodiment, is adapted to permit continuouswashing of the crystals recovered. Carbon tetrachloride from source 41is passed vby Way of line 42 and valved line 43 into centrifuge 38 toremove adhering mother liquid from the crystals. The washed, essentiallyvpure product crystals of tetrachloro-p-xylene are removed to reactor 11by way of lines 19 and 16; or entirely or in part the mother liquor fromline 51 may be withdrawn from the system by way of valved line 52.

Makeup carbon tetrachloride is introduced into the Y system fromsolution 41 by way of line 42 'and' valved line 53.

Example The reactor consisted of a 3-neck, round bottom flask withU-shaped side arm about 2/3 of Way up from the days.

bottom of ask. The ask was equipped with chlorine addition tube, inletfor filtrate, water-jacketed stirrer, thermometer and water-cooledcondenser. Chlorine was led from chlorine cylinder through a calibratedflowmeter to a trap and then to the reactor.

Reaction solution was drawn off continuously through the U-shaped sidearm and led to the top of `the crystallizer. Crystallizer was made from11/2 inch glass tubing and was 30 inches long. The top was fitted withan S-mm. take-oli tube and lil-mm. tube extending from the center 12inches into the ll/z-inch tube. The bottom 6 inches of the 11b-inch tubeywas tapered and iitted with aV large opening stop cock. After the rstday of operation, the crystallizer served as `a hold-up tank from whichthe solution was withdrawn when it became full. The solution was thencooled in an ice-water bath and then ltered to recover the product. Theltrate was led to a hold-up tank from which it was pumped to thereactor. The hold-up tank consisted of pear-shaped separatory funnel of500 ml. capacity. The pump was a bellows-type and was adjusted to pumpabout 600 ml. of carbon tetrachloride per hour.

The reactor was charged with 53 g. of p-xylene (0.5 mole, 98.5% purity),500 ml. of carbon tetrachloride, 2 g. of 20-mesh iron filling and 3 g.of ferrie chloride. Chlorine was passed into the solution at one moleper hour for 1.75 hours to convert half of the initial charge ofp-xylene to tetrachloro-xylene and half to trichloro- Xylene. After thisperiod, the reaction was put into continuous operation. The hold-upflask was lled with 500 m1. of carbon tetrachloride and 26 g. ofp-Xylene (1A mole), and pumped to the reactor in about one hour. Carbontetrachloride was added to the hold-up tank periodically to keep thesystem full. Each hour of operation, 26 g. of p-xylene was added to thehold-up flask. Cool reaction solution was withdrawn periodically fromthe crystallizer and filtered. In the latter part of the experiment, thereaction solution was cooled further in ice-water bath before filtering.Filtrate was returned to the hold-up flask. The reaction was run forfour hours the rst day and for eight hours each for thel next twoAdditional ferric chloride catalyst (4 g.) was added after 16 hours ofoperation. The product consisted of straw-colored, ne needles.

Thus having described the invention. what is claimed is:

l. A process for making tetrachloro-p-xylene which process comprises (l)chlorinating at a temperature between Iabout 40 C. and about 150 C. aliquid feed selected from the class consisting of p-xylene and lowercbloro-p-Xylene in the presence of a normally liquid chlorinatedaliphatic hydrocarbon containing from 1 to 4 carbon atoms and at leastone chlorine atom, to obtain a solution of chlorinated p-xylene in saidchlorinated hydrocarbon, said chlorinated p-xylene consisting of tetrachloro-p-xylene and a mixture of monochloro-p-Xylene, dichloro-p-xyleneand trichloro-p-xylene, (2) cooling said solution to a temperature suchthat crystals of tetrachloro-p-xylene are formed, as essentially theonly solid product, and (3) separating said solid product from liquidsolution of reduced tetrachloro-p-xylene content.

2. The process of claim l wherein said chlorinated hydrocarbon is carbontetrachloride.

3. The process of claim 1 wherein said chlorinated hydrocarbon istetrachloroethylene.

4. The process of claim 1 wherein said chlorinated hyd-rocarbon ischloroform.

5. The process of claim l wherein said chlorinated hydrocarbon istetrachloroethane.

6. The process of claim l wherein the chlorine usage is adjusted toproduce a solution containing tetrachlorop-xylene in an amount on theorder of the solubility in said solution at the chlorination zonetemperature.

7. The process of claim 6 wherein said chlorinated hydrocarbon is carbontetrachloride, said chlorination zone temperature is about reduxtemperature at about atmosesfin pheric pressure and said solution iscooled to about ordinary atmospheric temperature.

8. The process of claim 6 wherein said solution from step 3 is recycledto the chlorination zone.

9. A process for making tetrachloro-p-xylene which process comprises (a)chlorinating at 4about reux temperature at about atmospheric pressure aliquid feed selected from the class consisting of p-xylene and lowerchloro-p-Xylene in the presence of liquid carbon tetrachloride to obtaina liquid solution consisting essentially of tetrachloro-p-Xylene and a'mixture of monochloro-pxylene, dichloro-p-xylene landtrichloro-p-Xylene, the chlorine usage being adjusted to provide asolution containing between about 7-10 grams of tetrachloro-pxylene per100 grams of carbon tetrachloride, (b) cooling said solution to atemperature between about 15 C. and 30 C. to produce crystals of solidtetrachloro-p- References Cited in the tile of this patent UNITED STATESPATENTS 1,934,675 Mills Nov. 7, 1933 2,721,224 Rosin Oct. 18, 19552,729,685 Weimer et al. Jan. 3, 1956 2,805,264 Kissling Sept. 3, 1957OTHER REFERENCES Rupp: Bern der deut, Chem. Gese1l., vol. 29, pp. 1625-8(1896).

1. A PROCESS FOR MAKING TETRACHLORO-P-XYLENE WHICH PROCESS COMPRISES (1)CHLORINATING AT A TEMPERATURE BETWEEN ABOUT 40*C. AND ABOUT 150*C. ALIQUID FEED SELECTED FROM THE CLASS CONSISTING OF P-XYLENE AND LOWERCHLORO-P-XYLENE IN THE PRESENCE OF A NORMALLY LIQAUID CHLORINATEDALIPHATIC HYDROCARBON CONTAINING FROM 1 TO 4 CARBON ATOMS AND AT LEASTONE CHLORINE ATOM, TO OBTAIN A SOLUTION OF CHLORINATED P-XYLENE IN SAIDCHLORINATED HYDROCARBON, SAID CHLORINATED P-XYLENE CONSISTING OFTETRACHLORO-P-XYLENE AND A MIXTURE OF MONOCHLORO-P-XYLENE,DICHLORO-PYLENE AND TRICHLORO-P-XYLENE, (2) COOLING SAID SOLUTION TO ATEMPERATURE SUCH THAT CRYSTALS OF TETRACHLORO-P-XYLENE ARE FORMED, ASESSENTIALLY THE ONLY SOLID PRODUCT, AND (3) SEPARATING SAID SOLIDPRODUCT FROM LIQUID SOLUTION OF REDUCED TETRACHLORO-P-XYLENE CONTENT.